GH4169合金变应变速率热变形过程动态再结晶动力学行为及建模

目的 研究变应变速率高温变形过程中GH4169合金动态再结晶行为和晶粒组织的演变机理.方法 在不同变应变速率工况下对GH4169合金进行高温压缩实验,分析了变形参数对动态再结晶行为与晶粒组织的影响规律,建立变应变速率工艺下GH4169动态再结晶动力学和晶粒尺寸预测模型.结果 随着第一阶段真应变的增加或第一阶段/第二阶段应变速率的升高,GH4169合金动态再结晶程度降低,动态再结晶晶粒细化,平均晶体尺寸减小;建立的动态再结晶动力学模型的实验值和预测值之间的平均绝对相对误差(EAARE)和相关系数(R)分别为5.12％和0.988,建立的动态再结晶晶粒尺寸预测模型的预测值与实验值之间的EAARE和R分别为5.79％和0.992.结论 对GH4169合金变应变速率高温变形过程中动态再结晶机理的研究,可用于指导GH4169合金时变工况下的高温塑性成形.     

ZK60镁合金热压缩变形行为

为了研究ZK60镁合金的热变形行为,采用Gleebe-1500热模拟机在变形温度为423～673K、应变速率为0.001～10s-1条件下对合金进行的热压缩试验.分析合金流变应力与应变速率、变形温度之间的关系,通过引入Z参数建立合金流变应力本构方程,并观察合金变形过程中的显微组织演变.结果表明:变形温度低于473K且应变速率大于0.1s-1时试样发生宏观开裂;在变形温度较高和应变速率较低时,合金真应力-真应变曲线具有动态再结晶特征.随变形温度升高和应变速率的降低流变应力减小,热压缩后的组织中再结晶现象越明显;应变速率越高,再结晶晶粒越细小.     

超超临界发电机组螺栓用镍基高温合金混晶组织均匀细化工艺

目的 消除典型镍基合金锻件中存在的严重混晶组织,从而提高锻件的力学性能.方法 提出"低温 δ相时效+高温连续降温退火"双级热处理工艺,研究该热处理工艺对混晶组织演变及高温性能的影响,揭示锻造混晶组织的均匀细化机制.结果 利用该工艺可以在提升再结晶形核速率的同时降低再结晶晶粒的生长速率,从而获得平均晶粒尺寸为5.82μm的均匀细小的晶粒组织(达到ASTM12级),并可保证合理的δ相残余含量.同时,晶粒组织的均匀细化使得合金的强度以及塑性等力学性能均较传统DA工艺得到较大的提升,其中650℃屈服强度较DA工艺提升了13.4％.结论 连续降温再结晶热处理工艺可以有效改善镍基高温合金锻件中的混晶状态,并显著提升合金的强度和塑性.     

NiPt15合金热变形行为及微观组织演变规律

本研究采用Gleeble-3500热模拟机对NiPt15合金高温热变形过程进行研究,设定NiPt15合金变形温度为950～1150℃,变形速率为0.01～3 s-1.通过分析热变形过程中NiPt15合金在不同条件下的真应力-应变曲线,建立了双曲正弦型Arrhenius本构关系模型,并拟合模型各参数对合金变形量的依赖性.通过对热变形组织及显微硬度的表征,研究试样各区域热变形组织的差异,分析温度、变形速率、lnZ对动态再结晶及材料维氏硬度的影响.结果表明:NiPt15合金真应力-应变曲线包括三种不同变化趋势,各变形速率下对应的趋势变化临界温度值不同;应变激活能不大于476.85 kJ/mol;升高温度并且降低变形速率能提高再结晶比例至完全动态再结晶,形核机制为非连续性动态再结晶,主要以晶界弓出和反复生成孪晶为再结晶晶粒提供形核位置;当lnZ小于38.89时,晶粒尺寸与lnZ呈负相关性,当lnZ大于38.89时,晶粒尺寸与lnZ关系不明显;硬度与lnZ在本次实验条件下呈正相关性.     

中间形变热处理对2A97铝锂合金组织和性能的影响

通过室温拉伸、晶间腐蚀、电子背散射衍射(EBSD)、透射电镜(TEM)等测试方法,对中间形变热处理过程中进行不同压缩变形量处理的2 A97铝锂合金厚板短横向室温拉伸性能、晶间腐蚀性能和合金的宏微观组织进行了系统研究.结果表明,随压缩变形量的增加,合金再结晶程度提高,强度和伸长率先增加后降低.压缩变形量为20％时,再结晶晶粒细小,晶粒内包含均匀弥散分布的δ'相,晶界处的δ'相断续分布,合金的拉伸性能最好,伸长率明显提高;压缩变形量为25％时,合金的耐晶间腐蚀性能最好.合金的拉伸性能和腐蚀性能是由晶粒形貌和析出相的数量及分布共同作用的结果.     

Inconel625合金的高温高速热变形行为

对Inconel625合金在1000-1200℃,应变速率为10-80 s~(-1)条件下的热模拟压缩实验结果进行分析,修正了实验中由于高速变形产生的热效应引起的真应力-真应变曲线上流动应力的误差,通过回归分析建立了Inconel625合金高温高速下的本构模型.变形后的微观组织分析结果表明,提高变形速率是细化最终晶粒尺寸的重要途径,但过高的变形速率容易产生残余孪晶。在适当的温度(1050℃)与应变速率(50 s~(-1))下,合金具有均匀而细小的理想组织。     

AZ31镁合金温变形对其性能影响的研究

为了研究温变形对铸态AZ31镁合金力学性能的影响,在210～300℃温度范围内对均匀化后的合金进行了不同程度的平面应变压缩,并根据微观组织的演变对其进行了分析.结果表明:随变形温度的升高,在相同的变形程度下晶粒有长大的趋势,其抗拉强度增量下降;在同一温度下变形,强度增量随着变形程度的增加而增大,变形到一定程度时,呈现减小的趋势.在210℃下变形,当ε达到2.07时,其抗拉强度最大可达305MPa,较铸态提高近50%.表明AZ31合金温变形时,通过形变强化与细晶强化的合理组合,可获得细小均匀的等轴组织,大幅度提高镁合金的强度.     

ZK60镁合金高温动态再结晶行为的研究

采用Gleeble-1500热模拟试验机进行压缩实验,研究了ZK60镁合金在变形温度为473～723K、应变速率为0.001～1s~(-1)范围内变形过程中的组织演变.分析了变形程度、变形温度、变形速率对其动态再结晶行为的影响,探讨了其动态再结晶的形核机制.结果表明:ZK60合金高温塑性变形时的主要软化机制为动态再结晶,变形温度623K,应变量超过0.24时,在原晶界处出现大量的动态再结晶晶粒,并形成易延展的剪切区.变形温度是影响ZK60合金动态再结晶晶粒尺寸的主要因素,变形温度高于623K时,动态再结晶晶粒超过25μm.ZK60合金动态再结晶晶核在晶界弓弯处形成,随着应变量增加,出现亚晶界合并长大,长条状亚晶快速长大以及在剪切带变形区形核等.     

不同晶粒尺寸钛合金高温压缩力学行为研究

为了解不同晶粒尺寸钛合金的高温变形力学行为,对α相平均晶粒尺寸分别为6、12μm和20μm的TC4钛合金进行了高温压缩试验,研究了晶粒尺寸和变形参数对TC4钛合金高温压缩力学行为的影响,建立了不同晶粒尺寸TC4钛合金的高温变形本构方程.研究表明:应变速率为10-4s-1时6μm的细晶钛合金出现超塑现象,应变速率在10-3～10-1s-1范围时,变形初期不同晶粒尺寸钛合金的流动应力符合Hall-Petch关系,由于细晶钛合金流动应力软化速度较快,变形至稳态阶段时细晶钛合金流动应力低于粗晶合金.     

准晶增强Mg-Zn-Y合金的ECAP变形组织及力学性能

镁及镁合金作为目前工业应用中最轻的结构材料之一,具有良好的应用前景,然而由于镁合金自身强度较低、抗氧化性能差以及高温抗蠕变性能差等问题,使其作为某些结构件的应用受到限制,为进一步扩大其应用,人们采用了多种方法来提高其综合力学性能.二十面体准晶相(简称Ⅰ-phase)由于其特殊的结构而具有优异的力学性能,如高强度、高硬度等,将Ⅰ-phase作为一种增强相引入到镁合金中可大大提高镁合金的力学性能,为新型镁合金的开发和实际应用提供了一种新途径.本文采用常规铸造法制备了含有粗大网状Ⅰ-phase和α-Mg两相组织的Mg-Zn-Y合金.研究了合金含量及Zn/Y比对Mg-Zn-Y合金显微组织和力学性能的影响,探讨了热处理工艺对合金中相析出行为及Ⅰ-phase热稳定性的影响.以时效处理后的Mg-Zn-Y合金为研究对象,研究了两种塑性变形工艺(常规热挤压和等径角挤压变形)对合金显微组织和力学性能的影响,并对合金的细化机制、断裂行为与强化机制进行了研究.研究结果表明,在Y含量为0.3%～2.0%(at),Zn含量为1.7%～6.0%(at)的富镁Mg-Zn-Y合金中,合金的铸态组织及相组成取决于Zn/Y比和Zn含量,Zn/Y比为6时,合金的铸态组织由α-Mg基体和晶界上富镁相与Ⅰ-phase两相共晶组织组成;在所研究的合金成分范围内,合金中Ⅰ-phase的形成及其体积分数与合金的凝固速度有关,采用快速凝固的方法得到的合金中,由于第二相的形核及长大受到抑制,形成的Ⅰ-phase的体积分数相对于常规铸造工艺下制备的合金中Ⅰ-phase的含量有所减少,同时发现,合金的极限抗拉强度和屈服强度随合金中Ⅰ-phase体积分数的增加而增加,但合金的延伸率略有降低;在400℃、24h的热处理工艺下,Mg95Zn4.3Y0.7合金基体上有球形Ⅰ-phase析出,且析出的Ⅰ-phase在随后的时效处理中表现出热稳定性;在190℃不同时效时间下合金基体中的析出相为密排六方结构的MgZn2相,其析出行为与Mg-Zn二元合金类似.Mg-Zn-Y合金的热挤压结果表明,通过挤压变形可以显著细化合金的晶粒组织,合金的晶粒大小可由变形前的40～60μm减小到8～15μm,在挤压过程中位于晶界的Ⅰ-phase被破碎并较均匀地分布在基体合金中,随着挤压比的增大和挤压温度的降低,晶粒进一步细化,Ⅰ-phase的弥散程度增加.挤压变形可以显著提高Mg-Zn-Y合金的强度、硬度和延伸率;随着挤压比的增大,合金的强度、硬度和延伸率均有所增加;在所研究的3种合金中,Mg95Zn4.3Y0.7合金在523K以25:1的挤压比挤压后,具有较高的力学性能,其极限抗拉强度为287MPa,屈服强度为203MPa,延伸率为14.1%.对于预挤压态Mg-Zn-Y合金的ECAP变形结果表明,ECAP对于预挤压态Mg-Zn-Y合金组织的细化是一个不断加强的过程,1道次ECAP变形后,在一些粗大晶粒之间分布着许多细小的晶粒,随变形道次的增加,原始粗大的晶粒消失,形成均匀细小的等轴晶粒,平均晶粒尺寸为1～3μm,同时在ECAP过程中Ⅰ-phase被破碎并呈弥散分布.ECAP变形1道次可以显著提高Mg-Zn-Y合金的抗拉强度、屈服强度和延伸率,Mg95Zn4.3Y0.7合金ECAP变形1道次后力学性能指标σb=331MPa,σ0.2=223MPa,δ=19.4%.Mg-Zn-Y合金以A、BA、Bc、C等4种不同工艺路线进行8道次ECAP变形后的显微组织差异不大,均形成细小的等轴晶粒;4种工艺路线在1～8道次的变形过程中,合金的力学性能变化不同,对于路径A和BA,随着变形道次的增加,合金的抗拉强度、屈服强度和延伸率变化幅度不大,对于路径BC和C,变形道次超过4次后,产生的变形织构的弱化作用导致合金的屈服强度迅速降低,但是合金仍保持较高的抗拉强度和延伸率.通过对ECAP变形过程中Mg-Zn-Y合金晶粒细化过程的分析,结合其力学性能的变化得出ECAP变形的细化机制和准晶相强化机制:ECAP对于准晶增强Mg-Zn-Y合金的细化机制主要是基体在不同变形路径下的连续剪切变形机制和准晶粒子对于基体的剪切及钉扎机制;准晶增强Mg-Zn-Y合金ECAP变形过程中存在3种强化机制:细晶强化、第二相粒子强化和位错强化,3种强化机制分别在ECAP变形的不同阶段起主导作用,在共同的强化作用下提高合金的强度.     

Estimation of Parameters of Universal Distribution of Moments of Failure of Products

A method is proposed for estimating the parameters of a mixture of exponential and Weibull distributions for which the accuracy of preliminary estimates obtained by graphical analysis is refined in accordance with the criterion of maximum likelihood. The efficiency of the proposed method is supported by the results of statistical modeling.     

Evaluation of optical properties of highly scattering media by moments of distributions of times of flight of photons

A novel method for the determination of the optical properties of tissue from time-domain measurements is presented. The data analysis is based on the evaluation of the first moment and the second centralized moment, i.e., the mean time of flight and the variance of the measured distribution of times of flight (DTOF) of photons injected by short (picosecond) laser pulses. Analytical expressions are derived for calculation of absorption and of reduced scattering coefficients from these moments by application of diffusion theory for infinite and semi-infinite homogeneous media. The proposed method was tested on experimental data obtained with phantoms, and results for absorption and reduced scattering coefficients obtained by the proposed method are compared with those obtained by fitting of the same data with analytical solutions of the diffusion equation. Furthermore, the accuracy of the moment analysis was investigated for a range of integration limits of the DTOF. The moment analysis may serve as a comparatively fast method for evaluating optical properties with sufficient accuracy and can be used, e.g., for on-line monitoring of optical properties of biological tissue.     

Assessment of intakes of mixtures of radionuclides

Australia has several uranium mines and a large number of mineral sand mines, with associated processing facilities. Exposures resulting from these mining and processing operations usually involve intakes of mixtures of radionuclides. This work describes the development of a suite of first order, linear compartment models, based on the ICRP Publication 66 respiratory tract model, and an analytical solution to the decay equations, for assessing the consequences of such intakes. The computer programs based on these models directly compute excretion, organ retention and organ and whole-body doses for intakes of either single radionuclides or any mixture of radionuclides belonging to the same radioactive decay chain. The intake can be via inhalation, ingestion or injection, and can be acute, chronic or of limited duration. The starting concentration and degree of secular (dis)equilibrium can be specified for each radionuclide. No assumptions need to be made about the relative magnitudes of the radioactive half-lives of the different nuclides.     

Estimation of potentialities of methods of summation of direct measurement errors

Conventional methods for summation of direct measurement errors are considered. Conditions under which these methods provide consistent results are stated. It is proposed to utilize for characteristic of the total error, its interval estimator or the half-sum of the value obtained by adding up its arithmetic and geometric random errors.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 10–12, April, 1995.     

Analysis of the rate of propagation of the wave of change of boiling modes

An approximate analytical expression is derived for the velocity of the front of the wave of change of boiling modes on a rod and on a plate. The impact of the Thomson effect and of the heater orientation in the gravity field is included. Adequate agreement is demonstrated between the derived relations and experimental data.     

空压机轴承箱蜗壳温度探头油封改造

由于空压机进气侧轴承箱蜗壳温度探头密封效果不好,使空压机及其后续管道受到油污染。后将温度探头的O形圈密封改为骨架油封,杜绝了轴承箱漏油问题。文章简介空压机的结构和技术参数,详细介绍了骨架油封的制作和优点。     

Determination of parameters of microstructural inhomogeneity of deformation of metals by the method of modeling

The article suggests a method of evaluating the microstructural inhomogeneity of deformation of metals by modeling. The method includes the measurement of deformations of metal according to meshes of a dividing grid with small base and the calculation of the distribution parameters of microdeformations in model representation. It is shown that the modeling method makes it possible objectively to evaluate the microinhomogeneity of deformation of metals independently of the chosen mesh size of the dividing grid. New structural characteristics are introduced: the base and wave of variation expressing the degree of crumbling or amalgamation of metal grains by inhomogeneity of deformation.Translated from Problemy Prochnosti, No. 7, pp. 40–44, July, 1991.     

Characteristics of mechanical properties of materials in studies of conditions of attainment of marginal states

It is shown that conditions of attainment of marginal states in the material of structural components are formulated on the basis of analysis of force and deformation criteria of formation and development of destruction. The parameters of these criteria are data on types of structural materials, standard and special characteristics of their mechanical properties, structural forms of considered elements of the equipment, and their operating stress loading. In this case, the construction of a system of state equations for describing interrelation of current damage, external actions, and responses to them is based on the concept of calculating variations in properties of materials at all stages of the design life cycle.     

Analysis of anisotropy of properties on the basis of studies of texture of coarse-grained ingots of thermoelectric materials

An analysis of anisotropy of the properties of a Bi₂Se_0.3Te_2.7 solid solution was carried out using construction of demonstrative surfaces for thermoelectric effectiveness and thermal expansion coefficients. It is shown that the texture is an important factor forming anisotropy of properties and technological fitness of ingots for manufacturing modules. Anisotropy of properties based on the studies of the ingot textures obtained using the float-zone method and Bridgman method (growing thermoelectric plates in a flat cavity) was studied.